1. Field of the Invention
The invention relates to a dental hand instrument, which has an elongate handle sleeve, at the front end of which there are disposed means for holding a treatment tool, for example a dental drill. Disposed inside the handle sleeve are means for driving the treatment tool, which means have at least two rotatably mounted shafts that are coupled to each other.
2. Related Technology
Such a dental hand instrument is already known, and is represented schematically in FIG. 7. Represented in this case is a so-called angled piece 100, in which the handle sleeve 101 is slightly offset in the central region. Disposed at the front end of the handle sleeve 101 is the head region 102, which is realized for rotatably receiving a treatment tool, for example a dental drill. The driving of the drill—not shown—is effected by means of a drive train, which, in the exemplary embodiment shown, has two shafts 105 and 106 that are coupled to each other. The rear shaft 105 in this case is coupled, at its back end, to a drive, for example an electric motor and, at the front end, is coupled to the front shaft 106 via a transmission 107. The rotation of the shafts is then transferred to the drill via a further transmission 108 at the head region 102. Furthermore, cavities and lines, for carrying media and/or light, extend through the handpiece. The drawing figure shows, for example, an optical waveguide 109, via which light is directed onto the treatment site to be treated by the drill.
In the case of such a handpiece 100, a distinction is made between the so-called functional region, i.e. the region in which the power train comprising the necessary elements is located, and the further cavities. The further cavities constitute spaces in which are located the lines for media, such as spray air and water, and the light line and joint gaps. It is necessary for a seal to be effected between the functional region and these further cavities.
The above-mentioned seal is necessary since, during a maintenance process for the handpiece 100, the functional region is flushed by means of positive pressure from the motor connection side. Ideally, the oil and cleaning fluid used for this purpose should emerge solely at the top of the head region 102. Leakages or connections between the functional region and the cavities have a very disadvantageous and adverse effect upon the manipulation of the instrument, since oil could emerge at joint gaps and, owing to the surface of the handle region having become oiled as a result, this makes it more difficult to manipulate the handpiece and, in addition, also requires increased re-oiling.
In particular, in the case of the angled handpiece represented in FIG. 7, this sealing is extremely difficult because of the large differences in the toothing diameters in the knee region, in which the two shafts 105 and 106 are coupled. Hitherto, this problem has been solved in that O-rings have been inserted facing outwardly at interfaces for the purpose of sealing. In addition, complex elastic shaped pieces have been used, or partial encapsulation of the connection point has been effected for the purpose of sealing. Such measures have been unsatisfactory, however, and in some cases have had the result of greatly impeding the assembly and disassembly of the handpiece or, in some cases, have even made this impossible.